The present invention relates to a record carrier feed device for continuously feeding record media in the form of sheets of paper in contact with the peripheral surface of a platen into a printing region, and more specifically to a record carrier feed device adapted for use in typewriters or printers for electronic data processing systems or word processors.
Record carrier devices of this type are expected to serve to bring a record carrier moving along with a platen into intimate contact with the peripheral surface of the platen, that is, to protect the record carrier from dislocation or slacks or bulges, especially in a printing region.
To attain this, these conventional devices are provided with guide means for guiding the record carrier toward the platen while restraining the record carrier from tangentially separating from the platen at a position where the record carrier is fed upward after passing in a forward feed direction through the printing region in which a print head and the like are arranged, facing the front side of the platen.
In one such prior art record carrier feed device, as shown in FIGS. 1 and 2, the bottom portion of a platen 100 is surrounded by a paper pan 101 and front and rear feed rollers 102 and 103 supported by the paper pan 101. As the platen 100 rotates, the two feed rollers 102 and 103 transport the record carrier 104 in a forward feed direction as indicated by the arrows.
The record carrier 104 is fed upward through a printing region 105 which is defined between the platen 100 and a print head (not shown) opposed to the front side (right-hand side in FIG. 1) of the platen 10. Then, the record carrier 104 is held intimately against the platen 100 by guide rollers 106.
As shown in FIG. 2, the guide rollers 106 are rotatably supported at intervals on a shaft 107 which extends parallel to the platen 100. The shaft 107 is supported at both ends by swing arms 108, and the guide rollers 106 are urged to press on the platen 100 by springs 109 which are fixed individually on the arms 108. During the feeding of the record carrier 104, the swing arms 108 are in their operative position where they cause the guide rollers 106 to be pressed against the platen 100 by the urging force of the springs 109. At the time of the insertion of the record carrier 104 prior to the feeding operation, a solenoid 110 connected to the swing arms 108 is excited to move the swing arms 108 to an inoperative position indicated by two-dot chain lines in FIG. 1. As a result, the guide rollers 106 are disengaged from the platen 100, allowing the leading edge of the record carrier 104 to pass between the guide rollers 106 and the platen 100.
After preparations are made for the insertion of the record carrier 104, the solenoid 110 is deenergized to shift the guide rollers 106 from inoperative position to operative position, causing the leading edge of the record carrier 104 in the position indicated by two-dot chain lines to be pressed intimately against the platen 100. This arrangement may protect the record carrier 104 in the printing region 105 from dislocation, slacks, or bulges.
Disclosed in Japanese Patent Disclosure No. 56-144983 and FIGS. 1 and 2 of U.S. Pat. No. 4,453,847 are alternative examples of record carrier which, like the above-mentioned device, are constructed so that guide rollers are caused to abut against a platen during record carrier feeding.
In the prior art devices described above, the contact pressure of a plurality of guide rollers on the peripheral surface of the platen is subject to variations attributed to errors in accuracy. Accordingly, the pressure applied to the record carrier becomes uneven, exerting a bad influence upon the feeding accuracy. Structurally, moreover, it is difficult to adjust the pressure of the guide rollers for uniformity. Thus, the working accuracy of the guide rollers can be improved only in a limited manner.
According to the device of this type, furthermore, it is necessary to release the guide rollers from the platen with every record carricr insertion, requiring troublesome operation. Devices with an automatic record carrier insertion function absolutely require a solenoid or other shift mechanism for the guide rollers and other mechanisms associated therewith, resulting in a complicated construction and increased manufacturing cost.
These problems will be additionally serious if a printer with the record carrier feed device of this type is to be used for so-called graphic printing in which the rotation of the platen is controlled not only for the forward feed direction but for the reverse feed direction to effect printing of graphic patterns or diagrams on the record carrier on the platen.
In FIGS. 3 to 6 of U.S. Pat. No. 4,453,847, there is disclosed a feed arrangement in which a rotatable guiding member in the form of a paddle wheel having a number of resilient blades is mounted in interference relationship to a platen so that the blades serve to capture the leading edge of a record carrier and redirect it toward the platen.
This arrangement is not, however, very high in durability since the edges of the blades repeatedly strike against the platen and bend. If the guiding member rotates untimely, moreover, the blades will fail to capture the leading edge of the record carrier, and their edges will possibly reject or double the leading edge of the record carrier. Such a situation would produce nonnegligible noises.